The following patent applications for related subject matter,
xe2x80x9cCYLINDRICAL METAL-AIR BATTERY WITH A CYLINDRICAL PERIPHERAL AIR CATHODExe2x80x9d U.S. patent application Ser. No. 09/215,820; now U.S. Pat. No. 6,274,261;
xe2x80x9cAIR MANAGER SYSTEMS FOR METAL-AIR BATTERIES UTILIZING A DIAPHRAGM OR BELLOWSxe2x80x9d U.S. patent application Ser. No. 09/216,026 pending,
xe2x80x9cDIFFUSION CONTROLLED AIR VENT WITH AN INTERIOR FANxe2x80x9d U.S. patent application No. 09/215,879 pending,
xe2x80x9cUNIFORM SHELL FOR A METAL-AIR BATTERYxe2x80x9d U.S. patent application No. 09/216,114, now U.S. Pat. No. 6,235,418;
xe2x80x9cLOAD RESPONSIVE AIR DOOR FOR A METAL-AIR CELLxe2x80x9d U.S. patent application Ser. No. 09/216,115, now U.S. Pat. No. 6,350,537;
xe2x80x9cGeometry Change Diffusion Tube For Metal-Air Batteriesxe2x80x9d U.S. patent application No. 09/216,273, now U.S. Pat. No. 6,342,314;
xe2x80x9cAIR-MANAGING SYSTEM FOR METAL-AIR BATTERY USING RESEALABLE SEPTUMxe2x80x9d U.S. patent Ser. No. 09/216,343, now U.S. Pat. No. 6,168,877; and
xe2x80x9cAIR DELIVERY SYSTEM WITH VOLUME-CHANGEABLE PLENUM OF METAL-AIR BATTERYxe2x80x9d U.S. patent application No. 09/216,660, now U.S. Pat. No. 6,346,341;
all of which are incorporated herein by reference, have been filed concurrently with the present application.
The present invention relates to metal-air batteries of the type that are supplied with reactive gas by an active air moving device, and more particularly relates to an air mover mechanism located in the cathode plenum space of one or more metal-air cells.
Generally described, a metal-air cell, such as a zinc-air cell, uses one or more air permeable cathodes separated from a metallic zinc anode by an aqueous electrolyte. During operation of the cell, oxygen from the ambient air is converted at the one or more cathodes to produce hydroxide ions. The metallic zinc anode is then oxidized by the hydroxide ions. Water and electrons are released in this electrochemical reaction to provide electrical power.
Initially, metal-air cells found limited commercial use in devices, such as hearing aids, which required a low level of power. In these cells, the air openings which admitted air to the air cathode were so small that the cells could operate for some time without flooding or drying out as a result of the typical difference between the outside relative humidity and the water vapor pressure within the cell. However, the power output of such cells was too low to operate devices such as camcorders, cellular phones, or laptop computers. Furthermore, enlarging the air openings of a typical xe2x80x9cbutton cellxe2x80x9d was not practical because it would lead to premature failure as a result of flooding or drying out.
In order to increase the power output of metal-air cells so that they could be used to operate devices such as camcorders, cellular phones, or laptop computers, air managers were developed with a view to providing a flow of reactive air to the air cathodes of one or more metal-air cells while isolating the cells from environmental air and humidity when no output is required. As compared to conventional electrochemical power sources, metal-air cells containing air managers provide relatively high power output and long lifetime with relatively low weight. These advantages are due in part to the fact that metal-air cells utilize oxygen from the ambient air as the reactant in the electrochemical process as opposed to a heavier material such as a metal or a metallic composition. Examples of air managers are shown in U.S. Pat. Nos. 4,913,983, 5,356,729, and 5,691,074.
A disadvantage of most air managers, however, is that they distribute air within a plenum adjacent to the air electrode, and the plenum requires an empty volume of space. Furthermore, an important component of a successful air manager is an air moving device, typically a fan or an air pump. In the past, air moving devices used in metal-air batteries have been bulky relative to the volume of the metal-air cells. As a result, space that could otherwise be used for battery chemistry to prolong the life of the battery must be used to create a plenum adjacent to the air electrode and to accommodate an air moving device. This loss of space presents a particular challenge in attempts to provide a practical metal-air cell in small enclosures such as the xe2x80x9cAAxe2x80x9d cylindrical size now used as a standard in many electronic devices.
In addition to being bulky, air moving devices used in metal-air batteries also consume energy stored in the metal-air cells that might otherwise be delivered as power output to a load. Therefore, while a key advantage of metal-air cells is their high energy density resulting from the low weight of the air electrode, this advantage is compromised by the space and power required for an effective air manager.
As stated previously, air managers have been developed with a view to isolating the metal-air cells from ambient air when no output is required. A factor contributing to the problem of isolating metal-air cells from the ambient air is the porosity of inexpensive plastics typically used for molding cases for containing components of the cells. The amount of water vapor that seeps through plastic walls of a cell can be on the same order of magnitude as the amount of water vapor that passes into the cell through one or two diffusion limiting isolation tubes. Utilizing less porous materials or coating the plastic walls to reduce transmission of gases would add significant expense to the cost of each cell.
Therefore, there has been a need in the art for an air manager incorporating an air moving device that occupies less of the volume available for battery chemistry, is usable with advanced systems for isolating the air electrodes when power is not being drawn from the metal-air cell, and consumes a relatively low amount of power. Also, there is a further need in the art of metal-air cells to reduce the significance of case wall porosity.
The present invention seeks to provide an improved air moving device for metal-air cells that occupies a minimal amount of the volume available for battery chemistry, is usable with advanced systems for isolating the air electrodes when power is not being drawn from the metal air cell, and consumes a relatively low amount of power.
In accordance with the invention, this object is accomplished by providing an air-moving device for supplying ambient air to the air electrodes of a metal-air cell which includes a variable volume enclosure surrounding a plenum adjacent to the air electrode, means for varying the volume of this enclosure, and one or more air passageways which allow air flow into and out of the enclosure while its volume is changing. The variable volume enclosure serves to isolate the electrode from the ambient air except through the air passageways and operates so that air flows into the enclosure when its volume is increasing (as a result of a decrease in pressure inside the enclosure) and out of the enclosure when its volume is decreasing increasing (as a result of an increase in pressure inside the enclosure). Thus, the air moving device brings in new ambient air and distributes it across the surface of the air electrode during operation of the metal-air cell.
In one embodiment of the invention, the air passageways comprise diffusion limiting passageways. The variable volume enclosure may be a rigid plate connected to a deformable wall that extends to the frame surrounding the electrodes of one or more cells. The air passageways may extend through the rigid plate or the deformable wall. In this embodiment, the volume of the enclosure is varied by alternately moving the rigid plate toward and away from the air electrode. The means for alternately moving the rigid plate toward the air electrode may be a linear actuator such as a line engaging the rigid plate and a fixed member below the rigid plate and means for selectively pulling the rigid plate toward the fixed member using the line. The means for alternately moving the rigid plate away from the air electrode may be a line engaging the rigid plate and the outer casing of the metal-air power supply and means for selectively pulling the rigid plate toward the outer casing using the line. The lines may be shape memory alloy wires and both the means for selectively pulling the rigid plate toward the outer casing and the means for selectively pulling the rigid plate toward the fixed member may be an electrical circuit connected to supply current through the wires to shrink their length. Alternatively, the means for selectively pulling the rigid plate toward the outer casing and the means for selectively pulling the rigid plate toward the fixed member may also comprise winches connected to reel in the lines. In a modified embodiment, the means for alternately moving the rigid plate away from the air electrode may be one or more spring members, such as foam blocks, positioned between the rigid plate and the air electrode.
In one embodiment, an indirect linear actuator is provided to move the plate. In this configuration, the lines may extend substantially parallel to the electrode and the means for selectively pulling the rigid plate toward the outer casing and the means for selectively pulling the rigid plate toward the fixed member may include a cam surface and a cam follower which transpose the movement of the rigid plate responsive to the movement of the lines into a direction substantially perpendicular to the electrode.
The air moving device may also include means for preventing the outward deformation of the deformable wall so that the volume of the variable volume enclosure decreases more efficiently as the rigid plate moves toward the electrode. The means for preventing the outward deformation of the deformable wall may include retaining structures which may be walls positioned outside the variable volume enclosure. Alternatively, the deformable walls may incorporate inwardly acting springs or elastic members to prevent outward bowing of the deformable wall.
In an alternative embodiment, the variable volume enclosure may be a collapsible bag with the air passageways extending through the collapsible bag. The means for alternately contracting and expanding the bag may be one or more lines engaging the bag; means for reducing an initial effective length of the lines to collapse the bag from an initial volume to a smaller volume; and means for returning the bag to the initial volume. The lines may be a plurality of shape memory wires retained to the bag; and the means for reducing an initial effective length of the lines may be an electrical circuit connected to supply current through the wires to shrink an initial diameter thereof. Or, the lines may be connected to a winch, as noted above. The means for returning the bag to the initial volume may be one or more spring members positioned to urge the bag back to its expanded shape, stretching the shape memory wires or unwinding the lines from a winch. Preferably, the bag comprises a two-ply material defining passageways in which the shape memory wires or winch-driven lines are captured, the wires moving longitudinally within the passageways.
Preferably, the panel and the deformable wall (or the entire bag of the second embodiment) are constructed of materials of very low porosity, to reduce the effect of higher porosity material that may be used for the outer case.
According to another embodiment, the present invention provides a cylindrical metal-air power supply, comprising a conductive cylindrical case body including a cylindrical case wall, a case bottom, and an anode current collector extending into the case body from the case bottom; a mixture of anode metal and electrolyte within the case body in contact with the anode current collector; an air cathode positioned around the mixture and spaced inwardly from an inner surface of the cylindrical case wall, a cylindrical cathode air plenum being formed inside the cylindrical case wall; a case cover including a terminal electrically connected to a cathode current collector of the air cathode and insulated from the conductive case body; an enclosure within the cathode air plenum around the air cathode; an air conduit connecting the interior of the enclosure to the atmosphere outside the case; and means for alternately contracting and expanding the volume of the enclosure within the cathode air plenum to move air in and out of the enclosure through the air conduit.
In one form of this embodiment, the air conduit comprises a diffusion limiting passageway. The means for alternately contracting and expanding the bag may be one or more lines engaging the bag, operated by means for reducing an initial effective length of the lines to collapse the bag from an initial volume to a smaller volume; and means for returning the bag to the initial volume. The lines may be a plurality of formed shape memory wires retained to the bag. In this case the means for reducing an initial effective length of the lines may be an electrical circuit connected to supply current through the wires to shrink an initial diameter thereof; and the means for returning the bag to the initial volume may be a plurality of arcuate wire springs retained to the bag. Preferably, the bag comprises a two-ply material defining passageways in which the shape memory alloy wires and the wire springs are captured, the wires and springs moving longitudinally within the passageways.
The bag of this embodiment preferably extends from an essentially sealed connection to the case body at a base of the anode current collector to cover the air cathode and anode mixture beneath the case cover. This optional construction avoids the need to form a sealed connection between the bag and the peripheral edge of the air cathode. Also, the power output of the battery can be high because of the large cylindrical air cathode area. The cell can be assembled easily by placing the bag over the anode current collector, dropping the cathode assembly into the bag, filling the interior of the cathode assembly with the anode paste, and sealing the bag over the top of the cathode assembly. If the bag is formed of a very low porosity material, and is sealed above and below the cell components, there is no need to have sealed joints or low porosity materials outside the bag.
Other objects, features and advantages of the present invention will become apparent upon reviewing the following detailed description of preferred embodiments of the invention, when taken in conjunction with the drawings and the appended claims.